A variety of products may be formed from filled plastics. For example, plastics may be formed into lumber replacements, as described in U.S. Pat. No. 5,539,027; components of window and door assemblies, as described in U.S. Pat. No. 5,486,553; or siding for building structures, as described in U.S. Pat. No. 6,122,877.
Fillers have been used in the plastic industry for almost 90 years. The reason most manufacturers use filled plastic is to reduce the price of the high cost of polypropylene and other plastics with lower cost fillers, such as wood flour, talc, mica, and fiberglass. Filling plastic with fiberglass can improve its characteristics by creating higher thermal stability and higher bending and rupture strengths. However, low cost fillers like wood flour can degrade some of the qualities of plastics and make it harder to process. Talc and mica provide some increase in strength to plastic, but also add weight and decrease the life of the extruder due to abrasion. Fiberglass adds considerable strength of the product, but at a substantial cost.
There are many disadvantages associated with existing plastics filled with plant material, such, such as wood or straw. A principal problem associated with the extrusion and injection of such plastics is that the particle size of the plant material used in this process is very small and is primarily ground wood. Otherwise, the viscosity of the mixture is too high to be extruded or molded efficiently. Moreover, extrusion or injection processes are further limited by the ratio of filler materials, such as wood, to the plastic that can be used. This puts undesirable constraints on the products that can be produced. Wood plastic composites typically use between 30% to 65% wood flour or fine wood saw dust mixed with simple plastics. Ratios higher than this cause both processing problems and overall performance degradation in areas of moisture absorption, rot, decay, moisture stability, and so on.
There remains a need for an inexpensive, biologically derived material that can reduce the cost and consumption of thermoactive materials and that performs better than a filler for products such as window and door assemblies, lumber replacements, siding for buildings, and other goods.